Electronic cigarettes (e-cigs) are marketed by promoting a variety of flavors, which are added to e-liquids in variable quantities. The use of flavors has significantly increased e-cig use among middle and high school students, increasing their risk of nicotine addiction and the associated cardiopulmonary diseases, brain disorders, and cancers. Popular e-cig flavors are odor molecules that are present in high doses in many e- liquid brands; as such, they behave as irritants. It is well-known that the inhalation of high levels of popcorn flavorings and odors causes respiratory irritation, inflammation, chronic rhinosinusitis, asthma, and obstructive lung diseases. While sharing the general properties of odors, flavors are unique in masking the unpleasant irritation caused by nicotine and toxicants in e-cig vapor. Further, the masking dampens airway protective reactions without reducing the harm of nicotine and toxicants, rendering the respiratory tract more vulnerable to chemical-induced injury and diseases. The general public is not aware of the negative health effects of flavor inhalation. Masking makes e-cigs more appealing. Much worse, it perceptually misleads the public to believe e-cigs are safe, leading to increased e-cig use and abuse and more resistance to FDA?s educational campaign discouraging youth e-cig use. However, flavor-mediated dose-dependent respiratory irritation and the sensory masking that attenuates toxicant responses have not been objectively determined, hindering FDA CTP regulation of their use limits. This application proposes research addressing the FDA CTP interest in health effects and behavior. Specifically, we will use mouse models to (1) determine the dose-dependent sensory irritation responses evoked by five popular flavors and three flavor mixtures. We will determine the levels of irritation by monitoring the evoked trigeminal nociceptive nerve responses using event related potentials (ERPs) recorded from the anterior nasal respiratory epithelium. ERP serves as an exposure biomarker indicating respiratory irritation and potential chemical insults. (2) We will also assess the degree of flavor-mediated attenuation of sensory responses to irritants and toxicants. We will use ERP and intracellular Ca2+ responses to objectively determine the attenuation by three flavors and one mixture at two different concentrations. We will further evaluate the masking by employing the novel approach of directly recording the trigeminal nociceptive nerve using mice expressing a Ca2+ sensor GCaMP3. Together, these studies and comparative evaluation will assess the degree of flavor-exposure-induced respiratory irritation and illnesses across several popular flavors and mixtures and the chemosensory evaluation of masking will inform FDA CTP of flavor-based e-cig use behavior and its previously unrealized harm to the airway. We expect that our data will directly support FDA CTP regulation of flavor use limits in e-cig manufacture and marketing, and thereby minimize the associated respiratory illnesses to protect public health.